A systematic analysis of the structure, function, and regulation of the pyruvate, alpha-ketoglutarate, and branched chain alpha-keto acid dehydrogenase complexes from microorganisms and mammalian tissues will be continued. The two regulatory enzymes, pyruvate dehydrogenase kinase and pyruvate dehydrogenase phosphatase, will be further characterized with respect to subunit structure and function. These enzymes, which regulate the activity of the mammalian pyruvate dehydrogenase complex by phosphorylation and dephosphorylation, have been obtained in a homogeneous state. Systematic studies will be continued on structural and mechanistic similarities and differences between the alpha-keto acid dehydrogenase complexes, using electron microscopy, limited proteolysis and X-ray diffraction.